ANKARA, June 25 (Reuters) - Turkey has accused Syria ofshooting down one of its military reconnaissance jets ininternational airspace without warning and summoned a NATOmeeting for Tuesday to agree a response to Syrian PresidentBashar al-Assad.

Turkey's cabinet was due to meet on Monday to discussFriday's incident, which lent a more threatening internationaldimension to the 16-month-old uprising against Assad. Britaincalled the attack over the eastern Mediterranean outrageous andsaid it stood ready to back strong action in the United Nations.

"Turkey has moved into action" both Milliyet and Vatannewspapers declared in headlines under the NATO flag.

Sabah newspaper columnist Mehmet Barlas said some werecalling Friday's attack a Syrian declaration of war. "We alreadyknow there is an 'undeclared war' being carried out betweenTurkey and Syria," he said, citing the presence of the Syrianopposition and Syrian refugees sheltering on Turkish soil.

Fierce fighting continued inside Syria, which has a 900 km(550 mile) border with Turkey, with rebel fighters killingdozens of soldiers in the last few days as they fought againstarmy attacks on towns and villages in central, north and easternSyria in the last several days, according to opposition sources.

Syrian tanks and artillery shelled the eastern city of Deiral-Zor, killing at least 20 people in the second day of heavybombardment in the country's main oil-producing region,opposition activists said.

"Regime forces have dismantled their roadblocks from insideof Deir al-Zor after incurring heavy losses from rebels. Theyhave withdrawn from residential areas and are now shelling thecity from the outskirts. The victims are mostly civilians," asource at a hospital in Deir al-Zor told Reuters.

The official state news agency said "terrorists" abducted astate-appointed head of clerics in Deir al-Zor and blew up anoil pipeline passing through the province.

The Syrian Network for Human Rights, an oppositionactivists' organisation that monitors the crackdown on the16-month revolt against Assad's rule, said loyalist forces onSunday killed another 70 people, mostly civilians and soldierswho had tried to defect, elsewhere in the country in shelling,military raids and summary executions in the provinces of Homs,Hama, Idlib, Deraa and suburbs of Damascus.

The intensification of the fighting has raised fears inTurkey of a flood of refugees and a slide into ethnic andreligious warfare that could envelop the region. Ankara, likethe West, is torn between a wish to remove Assad and the fearthat any armed intervention could unleash uncontrollable forces.

WASHINGTON CONDEMNS ATTACK

U.S. Secretary of State Hillary Clinton called the attack"brazen and unacceptable" and said Washington would cooperateclosely with Ankara to promote a transition in Syria. Spanishgovernment sources said European Union foreign ministers wouldalso discuss the incident at a Luxembourg meeting on Monday.

While Turkish newspapers have railed against Assad, Erdogan,not always known for his emotional restraint, has eschewedbellicose rhetoric.

The prime minister, who turned against former ally Assadbitterly after he refused his advice to bow to demands fordemocratic reform, seemed to back away from any suggestion of anarmed response. If he sought some kind of retaliation from theNATO meeting set for Tuesday, he could have invoked anotherarticle on mutual defence. That he did not suggests the reactionwill remain at least for now on the diplomatic stage.

The foreign ministry said Turkey knew where the wreckage ofthe RF-4 Phantom jet lay, 1,300 metres (4,265 feet) under water,but had not yet found it. Minister Ahmet Davutoglu said thesearch continued for the two crew.

He said the jet had been clearly marked as Turkish anddismissed Syria's assertion it had not identified the aircraft,flying low and very fast, before opening fire.

RUSSIAN VETO

Some analysts said the aircraft could have been testingSyria's Russian-supplied radar and air defences, which would bean obstacle to any possible Western armed action.

Russia, which along with Iran is Damascus's chief ally, hasprovided most of Syria's arms and has access to a deep waternaval base in the country.

Davutoglu said he planned to set out Turkey's case to theU.N. Security Council where Western powers are seeking, againstRussian and Chinese opposition, to push through a motion thatcould allow stronger measures against Assad.